Fan motor

ABSTRACT

A fan motor may include a rotor part having a drive magnet, and a stator part having a drive coil and rotatably holding the rotor part. The rotor part may include a rotor yoke to which the drive magnet is fixed on an inner peripheral side of the rotor yoke, an impeller which is provided with a plurality of blades and which is disposed on an outer peripheral side of the rotor yoke, and a hub for fixing the impeller. The impeller is provided with a held part which is sandwiched between and held by the rotor yoke and the hub in an axial direction. The held part is abutted with an upper face of a bottom part of the rotor yoke and a lower face of a plate part of the hub, and the held part is held by the rotor yoke and the hub in the axial direction

CROSS REFERENCE TO RELATED APPLICATION

The present invention claims priority under 35 U.S.C. §119 to Japanese Application No. 2008-91712 filed Mar. 31, 2008 the entire contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

An embodiment of the present invention may relate to a fan motor.

BACKGROUND OF THE INVENTION

A fan motor for cooling has been conventionally mounted on an electronic apparatus for radiating heat generated in its inside. The fan motor has been known which includes a rotor part having a rotor magnet and a stator part having a coil (see, for example, Japanese Patent Laid-Open No. 2007-244045). In the fan motor described in the Patent Reference, a rotor part includes an impeller, which is made of resin and provided with a blade part, and a rotor yoke to which a rotor magnet is fixed on its inner peripheral face. The rotor yoke is press-fitted and fixed to an inner peripheral side of the impeller in the fan motor.

With a higher performance of an electronic apparatus in recent years, a higher cooling ability is required in a fan motor. In other words, performance for speedily radiating heat at a higher temperature is required in a fan motor and thus demand for high-speed rotation of the fan motor has been increased. However, like a fan motor as described in the Patent Reference, when a rotor yoke is press-fitted on the inner peripheral side of the impeller, unless a press-fitting margin of the rotor yoke to the impeller is increased to obtain a larger holding force by which the rotor yoke holds the impeller, slip may occur between the impeller and the rotor yoke due to a centrifugal force occurred when the fan motor is rotated at a high speed. On the other hand, when a press-fitting margin of the rotor yoke is increased larger, the impeller may be cracked due to a difference of the coefficients of thermal expansion of the rotor yoke and the impeller.

SUMMARY OF THE INVENTION

In view of the problems described above, at least an embodiment of the present invention may advantageously provide a fan motor in which a holding force between a rotor yoke and an impeller is increased while preventing cracking of the impeller.

According to at least an embodiment of the present invention, there may be provided a fan motor including a rotor part, which includes a drive magnet, and a stator part which includes a drive coil and rotatably holds the rotor part. The rotor part includes a rotor yoke to which the drive magnet is fixed on its inner peripheral side, an impeller which is provided with a plurality of blades and disposed on an outer peripheral side of the rotor yoke, and a hub for fixing the impeller. The impeller is provided with a held part which is sandwiched between and held by the rotor yoke and the hub in an axial direction.

Further, in accordance with an embodiment of the present invention, the rotor yoke is formed in a bottomed cylindrical shape having a bottom part, the hub is provided with a circular plate part, and the held part is abutted with an upper face of the bottom part of the rotor yoke and a lower face of the circular plate part of the hub, and the held part is sandwiched between and held by the rotor yoke and the hub in the axial direction. In addition, in accordance with an embodiment of the present invention, the held part is formed in a flat face shape substantially perpendicular to the axial direction. Further, in accordance with an embodiment of the present invention, the impeller is formed in a bottomed cylindrical shape having a bottom part, a step-shaped circular hole which is structured of a large diameter hole that is located on an upper side in the axial direction and a small diameter hole whose diameter is smaller than the large diameter hole and located on a lower side in the axial direction is formed at a center of the bottom part of the impeller so as to penetrate in the axial direction, and the held part is a flat part which is formed between a peripheral face of the large diameter hole and a peripheral face of the small diameter hole and which is sandwiched between and held by the rotor yoke and the hub in a state that an upper face of the bottom part of the rotor yoke is abutted with a lower face of the flat part and a lower face of the circular plate part of the hub is abutted with an upper face of the flat part.

In the fan motor in accordance with an embodiment of the present invention, the held part of the impeller is sandwiched between and held by the rotor yoke and the hub in the axial direction. Therefore, a contacting area of the rotor yoke with the held part of the impeller is increased and thus a frictional resistance between the rotor yoke and the impeller is increased and a holding force with which the rotor yoke holds the impeller is increased. Further, the held part is sandwiched between and held by the rotor yoke and the hub in the axial direction and thus, even when coefficient of thermal expansion of the rotor yoke is different from coefficient of thermal expansion of the impeller, a difference of deformation amounts at the time of thermal deformation can be relieved in the radial direction. Therefore, according to an embodiment of the present invention, cracking of the impeller can be prevented.

In accordance with an embodiment of the present invention, the hub is formed with a protruded part protruding toward the rotor yoke in the axial direction, the held part is formed with an arrangement hole in which the protruded part is disposed, the rotor yoke is formed with an engaging hole with which the protruded part is engaged, a tip end of the protruded part which is disposed at an edge of the engaging hole is protruded in the axial direction with respect to the engaging hole and formed as a caulking fixed part with which the hub and the rotor yoke are fixed to each other by caulking, and the caulking fixed part is fixed to the rotor yoke by caulking. According to this structure, the rotor yoke and the hub which sandwich and hold the held part of the impeller are directly fixed to each other and thus a holding force for the impeller is increased effectively. Therefore, the impeller is held in a stable state.

In accordance with an embodiment of the present invention, the hub is formed with an abutting part which is abutted with the stator part to restrict movement of the rotor part in the axial direction, and the abutting part is protruded in the same direction as the protruded part and protruded in the axial direction with respect to the protruded part. Further, in accordance with an embodiment of the present invention, the tip end of the protruded part is a projecting part which is formed in a cylindrical shape and a tip end of the projecting part is used as the caulking fixed part. According to this structure, the stator part does not abut with the caulking fixed part and thus damage of the caulking fixed part caused by abutting with the stator part is prevented. Accordingly, the impeller can be surely held in a stable state by means of that the rotor yoke and the hub are fixed to each other by caulking.

In accordance with an embodiment of the present invention, the rotor yoke is formed in a bottomed cylindrical shape, the protruded part which is formed in a substantially cylindrical shape is formed at a center of the hub so as to protrude in the axial direction toward the rotor yoke, a center of the held part is formed with a circular arrangement hole in which the protruded part is disposed, a center of a bottom part of the rotor yoke is formed with a circular engaging hole with which the protruded part is engaged, the protruded part is press-fitted to the engaging hole and abutted with a peripheral face of the engaging hole, and the rotor yoke and the hub are positioned each other with an outer peripheral face of the protruded part and a peripheral face of the engaging hole as reference. According to this structure, the rotor yoke is easily positioned in the radial direction by using a part of the hub.

In accordance with an embodiment of the present invention, the arrangement hole and the engaging hole are formed in the same diameter, and the protruded part is press-fitted to the arrangement hole and abutted with a peripheral face of the arrangement hole. According to this structure, the impeller is easily positioned in the radial direction by using a part of the hub.

In accordance with an embodiment of the present invention, the hub is formed of metal, and a rotation shaft structuring the rotor part is press-fitted and fixed to the hub. According to this structure, concentricity of the rotation shaft fixed to the hub with the rotor yoke is easily enhanced.

In accordance with an embodiment of the present invention, a plurality of ribs are formed which are protruded from at least one of an inner peripheral face of the impeller and an outer peripheral face of the rotor yoke in a radial direction with a predetermined interval. The rotor yoke is press-fitted to the impeller so that one of the inner peripheral face of the impeller and the outer peripheral face of the rotor yoke is abutted with end parts in the radial direction of the ribs, and a gap space is formed between the inner peripheral face of the impeller and the outer peripheral face of the rotor yoke. According to this structure, even when stress occurs in the impeller due to a centrifugal force, thermal expansion or the like occurred at the time of high-speed rotation, the gap space between the inner peripheral face of the impeller and the outer peripheral face of the rotor yoke serves as a relief part for the stress. Therefore, an excessive stress is not applied to the impeller and cracking of the impeller is prevented.

In accordance with an embodiment of the present invention, the impeller is formed of resin in a bottomed cylindrical shape, the rotor yoke is formed in a bottomed cylindrical shape having a bottom part which is abutted with the bottom part of the impeller, and the rib is formed on the inner peripheral face of the impeller so as to reach at least to a boundary portion between the bottom part of the impeller and the inner peripheral face of the impeller. Further, in accordance with an embodiment of the present invention, the bottom part of the impeller is formed with radial ribs extending from end parts of the ribs toward a center of the bottom part of the impeller so as to protrude in the axial direction, and the bottom part of the rotor yoke is abutted with the radial ribs. According to this structure, even when the bottom part of the rotor yoke is abutted with the bottom part of the impeller to position the rotor yoke in the axial direction, a thickness of the bottom part of the impeller may be set arbitrarily. Therefore, wall thicknesses of respective portions of the impeller formed of resin can be roughly equalized and thus shrinkage at the time of resin molding can be prevented.

Other features and advantages of the invention will be apparent from the following detailed description, taken in conjunction with the accompanying drawings that illustrate, by way of example, various features of embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described, by way of example only, with reference to the accompanying drawings which are meant to be exemplary, not limiting, and wherein like elements are numbered alike in several Figures, in which:

FIG. 1 is a cross-sectional view showing a schematic structure of a fan motor in accordance with an embodiment of the present invention.

FIG. 2 is a perspective view showing a rotor part in FIG. 1 which is viewed from a lower side.

FIG. 3 is a bottom view showing the rotor part in FIG. 1.

FIG. 4 is an exploded perspective view showing the rotor part in FIG. 1 which is viewed from a lower side.

FIG. 5 is an exploded perspective view showing the rotor part in FIG. 1 which is viewed from an upper side.

FIG. 6 is a cross-sectional view showing a schematic structure of a rotor part in accordance with another embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a cross-sectional view showing a schematic structure of a fan motor 1 in accordance with an embodiment of the present invention. FIG. 2 is a perspective view showing a rotor part 4 in FIG. 1 which is viewed from a lower side. FIG. 3 is a bottom view showing the rotor part 4 in FIG. 1. FIG. 4 is an exploded perspective view showing the rotor part 4 in FIG. 1 which is viewed from a lower side. FIG. 5 is an exploded perspective view showing the rotor part 4 in FIG. 1 which is viewed from an upper side. In FIGS. 2 through 5, a drive magnet 14 is not shown. Further, in this specification, the “X1” direction in FIG. 1 is referred to as an “upper side” and the “X2” direction is referred to as a “lower side”.

The fan motor 1 in this embodiment is a motor for cooling, for example, for radiating heat generated in the inside of an electronic apparatus. As shown in FIG. 1, the fan motor 1 includes a case body 2, and a stator part 3 and a rotor part 4 which are disposed in an inside of the case body 2. The stator part 3 is fixed to the case body 2. The rotor part 4 is rotatably held by the stator part 3.

The stator part 3 includes a bearing holder 6 which is formed in a roughly cylindrical shape, two bearings 7 which are disposed on an inner peripheral side of the bearing holder 6, a stator core 8 which is fixed on an outer peripheral face of the bearing holder 6, and a drive coil 9 which is wound around the stator core 8.

A lower end side of the bearing holder 6 is fixed to a stator fixing part 2 a which is formed on a lower side of the case body 2. Further, an inner peripheral face of the bearing holder 6 is formed with a protruded part 6 a which protrudes inside in a radial direction. One of two bearings 7 is disposed in the inside on the lower side of the bearing holder 6 in a state that its upper face is abutted with the protruded part 6 a. Further, the other bearing 7 is disposed in the inside on an upper end of the bearing holder 6 in a state that its lower face is abutted with an upper end of a compression coil spring 10 whose lower end is abutted with the protruded part 6 a. In other words, the protruded part 6 a serves as a positioning part for determining the positions of the bearings 7 which are disposed up and down.

The stator core 8 is, for example, a laminated core which is formed by means of that thin plates made of magnetic material are laminated on each other. The stator core 8 is formed with a plurality of salient pole parts around which the drive coil 9 is wound so as to protrude outside in the radial direction.

The rotor part 4 includes an impeller 12 having a plurality of blades 12 a, a hub 21 for fixing the impeller 12 and a rotation shaft 13 rotating together with the impeller 12, a drive magnet 14 which is formed in a cylindrical shape, and a rotor yoke 15 to which the drive magnet 14 is fixed.

Two positions of the rotation shaft 13, i.e., its upper side and lower end, are rotatably supported by two bearings 7. An upper end of the rotation shaft 13 is fixed to the hub 21. Further, the lower end side of the rotation shaft 13 is formed with a fixing groove 13 a to which a retaining ring 16 for preventing coming-out of the rotation shaft 13 from the bearing 7 is fixed. The retaining ring 16 fixed to the fixing groove 13 a is abutted with a lower face of the bearing 7 which is disposed on the lower side. In this embodiment, as described below, the impeller 12 is sandwiched between and held by the rotor yoke 15 and the hub 21 in an axial direction and thus the impeller 12 is fixed to the rotor yoke 15, and the rotor yoke 15 and the hub 21 are fixed to each other by caulking. In other words, in this embodiment, the impeller 12 is fixed to the rotation shaft 13 through the hub 21.

The rotor yoke 15 is formed of magnetic material. The rotor yoke 15 in this embodiment is formed of an electro-galvanized steel plate (SECC). Further, the rotor yoke 15 in this embodiment is formed by drawing work of a flat plate of SECC. The rotor yoke 15 is formed in a substantially bottomed cylindrical shape having a bottom part 15 a. Specifically, the rotor yoke 15 is structured of the bottom part 15 a, a small diameter cylindrical part 15 b whose upper end is connected with the bottom part 15 a, and a large diameter cylindrical part 15 c whose upper end is connected with the small diameter cylindrical part 15 b and whose inner diameter and outer diameter are larger than the small diameter cylindrical part 15 b. A center of the bottom part 15 a is formed with a circular engaging hole 15 d with which a tip end side of a protruded part 21 b formed in the hub 21 is engaged.

The drive magnet 14 is fixed on an inner peripheral face of the large diameter cylindrical part 15 c. Specifically, the drive magnet 14 is fixed on an inner peripheral face of the large diameter cylindrical part 15 c in a state that its upper end is abutted with a stepped part 15 f formed at a boundary portion between the small diameter cylindrical part 15 b and the large diameter cylindrical part 15 c. In this embodiment, as shown in FIG. 1, the inner peripheral face of the drive magnet 14 is disposed on an outer side of the inner peripheral face of the small diameter cylindrical part 15 b in the radial direction and thus the drive magnet 14 does not protrude on the inner peripheral side with respect to the small diameter cylindrical part 15 b. In this embodiment, the drive magnet 14 fixed to the rotor yoke 15 is disposed on an outer side of the stator core 8 in the radial direction so as to face each other. In other words, the fan motor 1 in this embodiment is an outer rotor type motor.

The impeller 12 is formed of resin. The impeller 12 in this embodiment is formed of polybutylene terephthalate (PBT). Further, the impeller 12 is formed in a roughly bottomed cylindrical shape having a bottom part 12 b abutting with an upper face of the bottom part 15 a of the rotor yoke 15. An outer peripheral face of the impeller 12 is formed with a plurality of blades 12 a formed in a thin plate shape which are protruded on an outer side in the radial direction. In this embodiment, eight blades 12 a are formed on the outer peripheral face of the impeller 12 with a substantially equal angular pitch.

A center of the bottom part 12 b of the impeller 12 is formed with a step-shaped circular hole, which is structured of a large diameter hole 12 f formed in an upper portion and a small diameter hole 12 g whose diameter is smaller than the large diameter hole 12 f and which is formed at a portion located on the lower side of the large diameter hole 12 f, so as to penetrate in the axial direction. As shown in FIG. 1, the large diameter hole 12 f and the small diameter hole 12 g are concentrically formed with the rotation center of the rotor part 4, i.e., the rotation shaft 13 as a center. Further, the diameter of the small diameter hole 12 g is set to be substantially equal to a diameter of the engaging hole 15 d which is formed in the bottom part 15 a of the rotor yoke 15. The small diameter hole 12 g of the impeller 12 in this embodiment is an arrangement hole to which the protruded part 21 b formed in the hub 21 is fitted.

A flat part 12 h which is formed in a flat ring shape so as to be substantially perpendicular to the axial direction is formed in the radial direction between a peripheral face of the large diameter hole 12 f and a peripheral face of the small diameter hole 12 g. In other words, the flat part 12 h is formed in a ring shape which protrudes on the inner side from the lower end of the large diameter hole 12 f in the radial direction, and the small diameter hole 12 g is formed at the center of the flat part 12 h. In this embodiment, the flat part 12 h is a held part which is sandwiched between and held by the rotor yoke 15 and the hub 21 in the axial direction.

As shown in FIG. 4 and the like, a plurality of ribs 12 d which are protruded on inner sides in the radial direction and formed in a substantially rectangular solid shape is formed on an inner peripheral face 12 c of a cylindrical part 12 k of the impeller 12. Specifically, a plurality of the ribs 12 d is formed on the inner peripheral face 12 c of the impeller 12 with a predetermined interval in a circumferential direction over the entire region of the cylindrical part 12 k of the impeller 12 in the axial direction. In this embodiment, eight ribs 12 d are formed with a substantially equal angular pitch so as to correspond to forming positions of the blades 12 a, i.e., on the inner sides of the blades 12 a in the radial direction. A thickness in the circumferential direction of the rib 12 d is roughly equal to a thickness of the blade 12 a.

As shown in FIG. 4, radial ribs 12 e which are formed in a substantially rectangular solid shape and connected with the ribs 12 d are formed on the lower face of the bottom part 12 b of the impeller 12 so as to protrude downward. Specifically, the radial ribs 12 e are radially formed from an upper end part of the rib 12 d formed on the inner peripheral face 12 c of the impeller 12 to the peripheral face of the small diameter hole 12 g.

The hub 21 is, for example, formed of metal such as brass. The hub 21 is provided with a circular plate part 21 a, which is formed in a circular plate shape and disposed on an upper side, and the protruded part 21 b whose diameter is smaller than the circular plate part 21 a and which is formed in a substantially cylindrical shape and protruded downward from the circular plate part 21 a. Further, a fixing hole 21 c to which the rotation shaft 13 is press-fitted and fixed is formed at the center of the hub 21 so as to penetrate in the axial direction.

An outer peripheral portion of the lower end of the protruded part 21 b is formed to be a projecting part 21 d formed in a cylindrical shape. Further, an abutting part 21 e for abutting with the upper face of the bearing 7 which is disposed on the upper side is formed on an inner side of the projecting part 21 d so as to protrude toward the lower side. Specifically, the abutting part 21 e in a substantially cylindrical shape is formed at an edge of the fixing hole 21 c. In this embodiment, as shown in FIG. 1, the abutting part 21 e is protruded lower than the protruded part 21 b. The abutting part 21 e is abutted with the bearing 7 to restrict movement of the rotor part 4 in the axial direction. Further, the projecting part 21 d and the abutting part 21 e are protruded lower than the engaging hole 15 d of the rotor yoke 15.

In this embodiment, the flat part 12 h of the impeller 12 is sandwiched between and held by the rotor yoke 15 and the hub 21 in the axial direction and thus the impeller 12 is fixed to the rotor yoke 15. In other words, the hub 21 has a function for fixing the impeller 12 to the rotor yoke 15. Specifically, as shown in FIG. 1, the circular plate part 21 a is disposed in the large diameter hole 12 f and the protruded part 21 b is disposed in the small diameter hole 12 g and the engaging hole 15 d. The flat part 12 h is sandwiched between and held by the lower face of the circular plate part 21 a abutting with the upper face of the flat part 12 h and the upper face of the bottom part 15 a of the rotor yoke 15 abutting with the lower face of the flat part 12 h (specifically, the radial rib 12 e) and, as a result, the impeller 12 is fixed to the rotor yoke 15.

Further, in this embodiment, the rotor yoke 15 and the hub 21 are fixed to each other by caulking by utilizing the tip end of the projecting part 21 d and the edge part of the engaging hole 15 d. In other words, as shown in FIG. 1, the tip end of the projecting part 21 d which is disposed at the edge part of the engaging hole 15 d is used as a caulking fixed part 21 f for fixing the rotor yoke 15 to the hub 21 by caulking. Specifically, a portion of the projecting part 21 d which is protruded lower than the engaging hole 15 d is the caulking fixed part 21 f.

In addition, in this embodiment, the protruded part 21 b is lightly press-fitted to the small diameter hole 12 g and the outer peripheral face of the protruded part 21 b is abutted with the peripheral face of the small diameter hole 12 g. In other words, in this embodiment, the impeller 12 and the hub 21 are positioned each other in the radial direction with the outer peripheral face of the protruded part 21 b and the peripheral face of the small diameter hole 12 g as references. Further, the protruded part 21 b (specifically, the projecting part 21 d) is lightly press-fitted into the engaging hole 15 d and the outer peripheral face of the protruded part 21 b is abutted with the peripheral face of the engaging hole 15 d. In other words, in this embodiment, the rotor yoke 15 and the hub 21 are positioned each other in the radial direction with the outer peripheral face of the protruded part 21 b and the peripheral face of the engaging hole 15 d as references. In this embodiment, a slight gap space is formed between the outer peripheral face of the circular plate part 21 a and the peripheral face of the large diameter hole 12 f.

As shown in FIG. 1, the impeller 12 other than the bottom part 12 b is disposed on the outer peripheral side of the rotor yoke 15. In this embodiment, as shown in FIG. 3, the impeller 12 is disposed on the outer peripheral side of the rotor yoke 15 in a state that inner side ends 12 m in the radial direction of the ribs 12 d are abutted with the outer peripheral face 15 e of the large diameter cylindrical part 15 c of the rotor yoke 15. Further, gap spaces 17 are formed with a substantially equal angular pitch between the inner peripheral face 12 c of the impeller 12 and the outer peripheral face 15 e of the rotor yoke 15.

The bearing 7 abutting with the abutting part 21 e is urged upward by an urging force of the compression coil spring 10. In other words, the hub 21 to which the rotation shaft 13 is fixed is urged upward by the urging force of the compression coil spring 10. Further, the retaining ring 16 abutting with the lower face of the bearing 7 which is disposed on the lower side is fixed to the lower end of the rotation shaft 13 and the upper face of the bearing 7 disposed on the lower side is abutted with the protruded part 6 a of the bearing holder 6. Therefore, coming-out of the rotation shaft 13 from the bearing 7 is prevented.

In the fan motor 1 structured as described above, firstly, the rotation shaft 13 is press-fitted and fixed to the hub 21. After that, the impeller 12 and the rotor yoke 15 are lightly press-fitted to the protruded part 21 b of the hub 21 and the rotor yoke 15 and the hub 21 are fixed to each other by caulking. After that, the drive magnet 14 is fixed on the inner peripheral face of the rotor yoke 15 and then rotation balance of the rotor part 4 is adjusted. In this embodiment, the outer peripheral face of the rotor yoke 15 is shaved to adjust the rotation balance of the rotor part 4. Specifically, two portions, i.e., the outer peripheral face of the rotor yoke 15 near the lower end of the impeller 12 and the outer peripheral face near the lower end of the rotor yoke 15 are shaved to adjust rotation balance of the rotor part 4.

As described above, in this embodiment, the flat part 12 h is sandwiched between and held by the rotor yoke 15 and the hub 21 in the axial direction and, in this manner, the impeller 12 is fixed to the rotor yoke 15. Therefore, contacting area of the rotor yoke 15 with the flat part 12 h and contacting area of the hub 21 with the flat part 12 h are comparatively increased. Therefore, a frictional resistance between the rotor yoke 15 and the impeller 12 and a frictional resistance between the hub 21 and the impeller 12 are increased and thus a holding force of the rotor yoke 15 for the impeller 12 can be enhanced.

Especially, in this embodiment, the hub 21 and the rotor yoke 15 which sandwich and hold the flat part 12 h are directly fixed to each other by caulking. Therefore, a holding force for the impeller 12 is increased effectively and thus the impeller 12 can be held in a stable state.

Further, in this embodiment, the flat part 12 h is sandwiched between and held by the rotor yoke 15 and the hub 21 in the axial direction and, in this manner, the impeller 12 is fixed to the rotor yoke 15. Therefore, even when coefficient of thermal expansion of the rotor yoke 15 is different from coefficient of thermal expansion of the impeller 12, a difference of deformation amounts at the time of thermal deformation can be relieved in the radial direction.

Especially, in this embodiment, the ribs 12 d are formed on the inner peripheral face 12 c of the impeller 12 and thus gap spaces 17 are formed between the inner peripheral face 12 c of the impeller 12 and the outer peripheral face 15 e of the rotor yoke 15. Therefore, even when stress occurs in the impeller 12 due to a centrifugal force, thermal expansion or the like occurred at the time of high-speed rotation, the gap spaces 17 serve as a relief part for the stress. Therefore, in this embodiment, even when the fan motor 1 is rotated at a high speed or, even when the fan motor 1 is used under a high temperature situation, an excessive stress which occurs in the impeller 12 can be relieved and cracking of the impeller 12 can be restrained.

Further, in this embodiment, the rotor yoke 15 is formed in a step-shaped cylindrical shape having the small diameter cylindrical part 15 b and the large diameter cylindrical part 15 c, and a gap space in the radial direction is formed between the outer peripheral face of the small diameter cylindrical part 15 b and the inner side ends 12 m in the radial direction of the ribs 12 d in the state that the impeller 12 is fixed to the rotor yoke 15. Therefore, stress occurring in the impeller 12 due to a centrifugal force, thermal expansion or the like occurred at the time of high-speed rotation may be relieved by utilizing the gap space in the radial direction.

In this embodiment, the abutting part 21 e formed in the hub 21 is protruded lower than the projecting part 21 d. Therefore, the stator part does not abut with the caulking fixed part 21 f and thus damage of the caulking fixed part 12 f caused by abutting with the stator part 3 is prevented. Accordingly, the impeller 21 can be surely held in a stable state by the rotor yoke 15 and the hub 21 which are fixed to each other by caulking.

In this embodiment, the hub 21 is formed of metal and the rotation shaft 13 is press-fitted and fixed to the hub 21. Therefore, concentricity of the rotation shaft 13 with the rotor yoke 15 which are fixed to the hub 21 is easily enhanced.

In this embodiment, the protruded part 21 b of the hub 21 is lightly press-fitted to the engaging hole 15 d of the rotor yoke 15 and abutted with the peripheral face of the engaging hole 15 d. Therefore, positioning of the rotor yoke 15 in the radial direction can be easily performed by using a part of the hub 21 and thus concentricity of the rotation shaft 13 that is press-fitted and fixed to the hub 21 with the rotor yoke 15 is easily enhanced. Accordingly, initial unbalanced quantity of the rotor part 4 can be reduced. Further, in this embodiment, the protruded part 21 b is lightly press-fitted to the small diameter hole 12 g of the impeller 12 and abutted with the peripheral face of the small diameter hole 12 g. Therefore, the impeller 12 in the radial direction can be easily positioned by using a part of the hub 21 and thus concentricity of the rotation shaft 13 that is press-fitted and fixed to the hub 21 with the impeller 12 is easily enhanced. Accordingly, initial unbalanced quantity of the rotor part 4 can be reduced.

In this embodiment, the ribs 12 d are formed so as to correspond to the forming positions of the blades 12 a. Therefore, shape of the impeller 12 including the blades 12 a is stable.

Although the present invention has been shown and described with reference to a specific embodiment, various changes and modifications will be apparent to those skilled in the art from the teachings herein.

In the embodiment described above, the hub 21 is provided with the circular plate part 21 a and the protruded part 21 b. However, for example, as shown in FIG. 6, the hub 21 may be structured of only the circular plate part 21 a. In this case, for example, the hub 21 and the rotor yoke 15 are press-fitted to the rotation shaft 13, and the flat part 12 h of the impeller 12 is sandwiched between and held by the hub 21 and the rotor yoke 15 in the axial direction and, as a result, the impeller 12 is fixed to the rotor yoke 15. Further, in this case, for example, the impeller 12 is lightly press-fitted to the rotation shaft 13. In FIG. 6, the same notational symbol is used in the same structure as the embodiment described above.

In the embodiment described above, the flat part 12 h which is sandwiched between and held by the hub 21 and the rotor yoke 15 over the entire circumference in the axial direction is formed in a flat face shape substantially perpendicular to the axial direction. However, the present invention is not limited to this embodiment. For example, an inclined part whose upper face and/or lower face is inclined in a direction perpendicular to the axial direction is sandwiched between and held by the hub 21 and the rotor yoke 15 in the axial direction.

In the embodiment described above, the protruded part 21 b is lightly press-fitted to the small diameter hole 12 g and the outer peripheral face of the protruded part 21 b is abutted with the peripheral face of the small diameter hole 12 g. However, the present invention is not limited to this embodiment. For example, the protruded part 21 b may be inserted into the small diameter hole 12 g so that the outer peripheral face of the protruded part 21 b is abutted with the peripheral face of the small diameter hole 12 g. Further, in the embodiment described above, the protruded part 21 b is lightly press-fitted to the engaging hole 15 d and the outer peripheral face of the protruded part 21 b is abutted with the peripheral face of the engaging hole 15 d. However, the protruded part 21 b may be inserted into the engaging hole 15 d so that the outer peripheral face of the protruded part 21 b is abutted with the peripheral face of the engaging hole 15 d.

In the embodiment described above, the hub 21 is formed of metal but the hub 21 may be formed of resin. When the hub 21 is formed of metal, weight of the hub 21 which is disposed at the center in the radial direction of the rotor part 4 is increased and thus rotation balance of the rotor part 4 is enhanced. Therefore, it is preferable that the hub 21 is formed of metal.

In the embodiment described above, a plurality of the ribs 12 d protruding toward inner sides in the radial direction is formed on the inner peripheral face 12 c of the impeller 12. However, the present invention is not limited to this embodiment. For example, a plurality of ribs protruding toward outer sides in the radial direction may be formed on the outer peripheral face 15 e of the rotor yoke 15 instead of the ribs 12 d or in addition to the ribs 12 d.

In the embodiment described above, eight ribs 12 d are formed on the inner sides in the radial direction of the blades 12 a with a substantially equal angular pitch. However, the present invention is not limited to this embodiment. For example, a plurality of the ribs 12 d may be formed at positions shifted from the corresponding inner sides in the radial direction to the blades 12 a and may be formed at a different angular pitch. Further, the number of the ribs 12 d is not limited to eight and the number may be more than 9 or may be 2 through 7.

In the embodiment described above, the rotation shaft 13 is fixed to the hub 21 and the rotation shaft 13 is rotated together with the impeller 12. However, the present invention is not limited to this embodiment. For example, a fixed shaft is disposed in the stator part 4 and the hub 21 may be rotatably supported by the fixed shaft. In other words, the fan motor 1 described above is a shaft rotatable type motor but the present invention may be applied to a shaft fixed type motor.

While the description above refers to particular embodiments of the present invention, it will be understood that many modifications may be made without departing from the spirit thereof. The accompanying claims are intended to cover such modifications as would fall within the true scope and spirit of the present invention.

The presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims, rather than the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. 

1. A fan motor comprising: a rotor part which includes a drive magnet; and a stator part which includes a drive coil and which rotatably holds the rotor part; wherein the rotor part comprises; a rotor yoke to which the drive magnet is fixed on an inner peripheral side of the rotor yoke; an impeller which is provided with a plurality of blades and which is disposed on an outer peripheral side of the rotor yoke; and a hub for fixing the impeller; wherein the impeller is provided with a held part which is sandwiched between and held by the rotor yoke and the hub in an axial direction.
 2. The fan motor according to claim 1, wherein the rotor yoke is formed in a bottomed cylindrical shape having a bottom part, the hub is provided with a plate part, and the held part is abutted with an upper face of the bottom part of the rotor yoke and a lower face of the plate part of the hub, and the held part is sandwiched between and held by the rotor yoke and the hub in the axial direction.
 3. The fan motor according to claim 2, wherein the held part is formed in a flat shape substantially perpendicular to the axial direction.
 4. The fan motor according to claim 3, wherein the impeller is formed in a bottomed cylindrical shape having a bottom part, a step-shaped circular hole which is structured of a large diameter hole that is located on an upper side in the axial direction and a small diameter hole whose diameter is smaller than the large diameter hole and that is located on a lower side in the axial direction is formed at a center of the bottom part of the impeller so as to penetrate in the axial direction, and the held part is a flat part which is formed between a peripheral face of the large diameter hole and a peripheral face of the small diameter hole and which is sandwiched between and held by the rotor yoke and the hub in a state that an upper face of the bottom part of the rotor yoke is abutted with a lower face of the flat part and a lower face of the plate part of the hub is abutted with an upper face of the flat part.
 5. The fan motor according to claim 1, wherein the hub is formed with a protruded part protruding toward the rotor yoke in the axial direction, the held part is formed with an arrangement hole in which the protruded part is disposed, the rotor yoke is formed with an engaging hole with which the protruded part is engaged, a tip end of the protruded part which is disposed at an edge of the engaging hole is protruded in the axial direction with respect to the engaging hole and formed as a caulking fixed part with which the hub and the rotor yoke are fixed to each other by caulking, and the caulking fixed part is fixed to the rotor yoke by caulking.
 6. The fan motor according to claim 5, wherein the hub is formed with an abutting part which is abutted with the stator part to restrict movement of the rotor part in the axial direction, and the abutting part is protruded in same direction as the protruded part and protruded in the axial direction with respect to the protruded part.
 7. The fan motor according to claim 5, wherein the tip end of the protruded part is a projecting part which is formed in a cylindrical shape and a tip end of the projecting part is used as the caulking fixed part.
 8. The fan motor according to claim 1, wherein the rotor yoke is formed in a bottomed cylindrical shape, a protruded part which is formed in a substantially cylindrical shape is formed at a center of the hub so as to protrude in the axial direction toward the rotor yoke, a center of the held part is formed with a circular arrangement hole in which the protruded part is disposed, a center of a bottom part of the rotor yoke is formed with a circular engaging hole with which the protruded part is engaged, the protruded part is press-fitted to the engaging hole and abutted with a peripheral face of the engaging hole, and the rotor yoke and the hub are positioned with an outer peripheral face of the protruded part and a peripheral face of the engaging hole as reference.
 9. The fan motor according to claim 8, wherein the circular arrangement hole and the circular engaging hole are formed in same diameter, and the protruded part is press-fitted to the circular arrangement hole and abutted with a peripheral face of the circular arrangement hole.
 10. The fan motor according to claim 1, wherein the hub is formed of metal, and a rotation shaft structuring the rotor part is press-fitted and fixed to the hub.
 11. The fan motor according to claim 1, further comprising a plurality of ribs which are protruded from at least one of an inner peripheral face of the impeller and an outer peripheral face of the rotor in a radial direction with a predetermined interval, wherein the rotor yoke is press-fitted to the impeller so that one of the inner peripheral face of the impeller and the outer peripheral face of the rotor yoke is abutted with end parts in the radial direction of the ribs, and wherein a gap space is formed between the inner peripheral face of the impeller and the outer peripheral face of the rotor yoke.
 12. The fan motor according to claim 11, wherein the impeller is formed of resin and formed in a bottomed cylindrical shape, the rotor yoke is formed in a bottomed cylindrical shape having a bottom part which is abutted with a bottom part of the impeller, and the rib is formed on the inner peripheral face of the impeller so as to reach at least to a boundary portion between the bottom part of the impeller and the inner peripheral face of the impeller.
 13. The fan motor according to claim 12, wherein the bottom part of the impeller is formed with radial ribs extending from end parts of the ribs toward a center of the bottom part of the impeller so as to protrude in the axial direction, and the bottom part of the rotor yoke is abutted with the radial ribs. 